Pickup arms

ABSTRACT

This invention relates to an improved phonograph pickup arm assembly affording a wide range of adjustments. In particular, the arm includes means for adjusting playing weight in which variation of playing weight is accompanied by automatic adjustment of a force correcting the side thrust of skating force at the stylus. The correcting force is produced by inclination of the pivotal axis of the arm by an angular amount about which produces an appropriate horizontally resolved part of the vertical force of the stylus. The pickup arm can be unplugged towards its inward end.

United States Patent Rohertson-Ailtman Web. 29, 11972 [54] HICKUP ARMS3,088,742 5/1963 Alexandrovich.... .....274/23 [72] Inventor: MasmirJohn kobensonflikman 3,219,351 11/1965 Sharper et al ..274/23 StokesSteymng Sussex England Primary ExaminerLeonard Forman [22] Filed: Mar.17, 1969 Assistant Examiner-Charles E. Phillips [2]] Appl NOJ 807,5W7Attorney Laurence E. Laubscher [57] ABSTRACT [30] Foreign ApplicationPriority Data This invention relates to an improved phonograph pickuparm Mar. 19, 1968 Great Britain ..13,318/68 bl ff ding a id range fadjustments. In particular, the arm includes means for adjusting playingweight in which [52] U.S. Cl. ..274/23 R va i ti n of playing weight isaccompanied by automatic ad- [511 p 3/10 justment of a force correctingthe side thrust of skating force Fleld of Search at the stylus. Thecorrecting force is produced inclinaion of the pivotal axis of the armby an angular amount about [56} References Cited which produces anappropriate horizontally resolved part of UNITED STATES PATENTS thevertical force of the stylus. The pickup arm can be un l 792 830 2/1931Goudy 274/23 plugged towards its inward end. 3,051,494 8/1962 Walton..274/23 18 Ciaims, 6 Drawing Figures Patented Feb. 29, 1972 3Sheets-Sheet 1 V U) AlaS fkfl R Cr S n-H KM INVENTOR BY W zem ATTORNEYPatented Feb. 29, 1972 I 3,645,541

3 Sheets-Sheet 2 INVENTOR ATTORNEY PICKUP ARMS This invention relates tosupport arms for gramophone pickups and has for its object to provide animproved construction of arm in which adjustments of the playingconditions can be readily effected.

\ Apickup arm for use with high-quality pickup cartridges must havecertain facilities of adjustment, and this is especially so where an armis intended for use with different heads or cartridges, of differentweights and playing weights. For example, it is essential that thecounterbalancing of the arm should be adjustable, to allow for differentweights of head or cartridge and it is also desirable that there shouldbe a separate means adjusting the playing weight of the cartridge,preferably by means which allows the playing weight to be indicated, andset or reset as desired.

Pickup arms used for pickups for gramophone reproduction are almostexclusively of the pivoted type, where the arm can pivot about avertical axis to allow the pickup stylus to traverse across the radiusof the gramophone record. With this type of arm, it is not possible forthe longitudinal axis of the pickup cartridge to be tangential to therecord groove at all radii as the pickup traverses the record. Tominimize the tracking error due to this fact it is the practice to makethe stylus overhang, that is, to make the distance from the pickupstylus to the arm pivot slightly greater than the distance from therecord center to the arm pivot. The axis of the cartridge is thendisposed at a suitable angle to the line forming the stylus and thevertical pivot axis.

This arrangement can be shown to cause a side thrust on the pickupstylus, in a direction towards the center of the record. Such a sidethrust is generally undesirable as it means the stylus is working in anonsymmetrical, biased condition with respect to the groove; it isparticularly undesirable when single roove stereophonic records arebeing played. The inclined side wall of the record groove gives the sidethrust a resolved part which tends to lift the stylus from the groove,and this requires an increase of playing weight of the stylus, which isalso undesirable.

The magnitude of the side thrust depends upon a number of factors, butfor any particular arm, the side thrust will be a fixed proportion ofthe frictional force or drag imposed on the stylus in the directionalong the record groove at the point of contact. The value of thisproportion is fixed by the dimensions of the pickup arm, in particularthe distance from the vertical pivot of the arm to the stylus tip, andthe overhang. The value of the proportion will also depend to someextent on the radius of the groove of the record which is beingreproduced, but it is convenient to take, as reference, a radius ofabout 4 inches, which is the center radius of the playing area of aconventional 12 inch record. For practical purposes, therefore, with agiven arm installation the ratio of the side thrust to the frictionalforce can be regarded as sensibly constant.

The frictional force at the stylus will be equal to the product of theplaying weight of the pickup, that is, the downward force at the stylus,and the coefficient of friction which exists between the stylus tip andthe record. This in turn depends on certain factors: the material of therecord, and the finish and tip radius of the stylus. With modernlongplaying vinyl records, and with a suitable stylus tip radius thecoefficient of friction for a given cartridge and stylus is reasonablyconstant.

In practice, with different pickup installations, it is found that theyside thrust lies in a range of about 0.15 to 0.30 times the playingweight. For a given pickup, the side thrust tends to be a fixedproportion of the stylus playing weight, so that if the playing weightis changed, there will be a corresponding change in the side thrust.

In the past, means have been suggested for imposing on the pickup aforce which is substantially equal and opposed to the side thrust. Forexample, a widely used expedient is a small weight suspended by a threadattached to the arm. Magnetic bias, and bias by means of small weightedarms have also been suggested but with all these forms of adjustment ithas been necessary to make a separate adjustment of the side thrustcounterbalancing force each time that an adjustment is made of theplaying weight.

One feature of a pickup an accordance with the present invention is thatmeans are provided whereby the playing weight of the pickup can beadjusted; means are also provided whereby a force is applied to balancethe side thrust and, in addition, it is arranged that any adjustment ofthe playing weight by the means afforded for changing playing weightalso changes the side thrust correcting force.

In a pickup arm of a type which is intended for use with differentcartridges arrangements are often made for unplugging the head,including the cartridge, and replacing it with another head andcartridge. The back of the head, for this purpose may include thenecessary mechanical coupling means, in conjunction with electrical plugand socket means for establishing the necessary electrical connectionsto the cartridge.

While this facility of head change is: a requirement, it adds to theweight of the head, which is undesirable. In accordance with anotherfeature of the invention, in a pickup arm construction the head is madeseparable, but the separable portion includes a substantial part ofthepickup arm. By this means the separable mechanical and electricalcouplings are disposed closer to the horizontal arm pivot axis, wherethe resultant increase of moment of inertia will be less.

Other features and advantages of the invention will appear from thefollowing description of an embodiment thereof,

given by way of example, in conjunction with the accompanying drawings,in which FIG. 1 is a plan view of a gramophone pickup and arm;

FIG. 2 is a side elevational view of the pickup and arm of FIG. ll;

FIG. 3 is a side elevational view, partly in section, on the line 3-3 ofFIG. 11;

FIG. 4 is a sectional view taken on the line 4-4 of FIG. 3;

FIG. 5 is a sectional view taken on the line 5-5 of FIG. 1, and

FIG. 6 is a fragmentary elevational view looking in the direction ofarrows 5-5 of FIG. l.

The pickup arm shown comprises a main base plate 10, in which is carrieda sliding bush ll, forming a bearing for a main support pillar 12. Thebase plate is adapted to be carried by a support plate 13 so as to bereadily detachable therefrom, and for this purpose the base plate hassecuring and locating pegs 114, which are adapted to engage in socketsK5 in the support plate. The pegs are split, so that they will eachengage a socket l5 accurately and with sufficient frictional grip tohold the base plate in position on the support plate in use. The supportplate is intended to be fastened to a motor board 16, for example byscrews 17.

The pillar 12 supports a pillar head assembly 20 from the rear end ofwhich is supported a cross shaft bearing sleeve 21. In this sleeve ahollow shaft 22 is mounted in miniature ball bearings 23. To one end ofthe shaft is secured a cap 24-, by

means of a screw 25, while the other end of the shaft carries a yoke 26,held by a hollow screw 27 and washer 28. Means are provided carefully toseal the bearings 23 against the ingress of dust or other foreignmaterial. It will be observed from FIG. 5 that the axis of shaft 22 isat an angle a to the horizontal.

The outer ends of the arm of yoke 26 support the pickup arm assemblyindicated generally at 30. This includes a bearing section 31 which ismounted in the arms of the yoke 26 by bearings arranged to provide apivotal movement which is substantially at right angles to the axis ofshaft 22. At its section 31, the pickup arm is hexagonal, as shown inFIGS. 1 and 5, and is pivotally mounted by precision ball bearings 32,fitting in the arms of the yoke, and pillar screws 33, threaded into thehexagonalrsection 31 of the arm. Caps 34 and sealing rings 35 areprovided to prevent ingress of any dust or the like to the bearings 32.

Rearwardly of the section 31, the arm has an extension 36 (FIG. 3) onwhich is arranged a cou'nterbalancing assembly.

munn nlun which permits the arm to be balanced about the axis of shaft22, and also about the axis defined by bearings 32. A sleeve 37 issupported from the rearward end 36 of the arm by means of three spacedgrommets 38 and a rubber plug 39; this provides a decoupling of massbetween the sleeve and the arm. A cap 40 is internally threaded andscrewed on the rearward part of the sleeve 37. A milled ring 41, whichhouses removable annular weights 42, is held frictionally on the outsideof cap 40 by means of a shaped nylon ring 43. When the milled ring 41 isrotated, the cap will be adjusted axially, to pennit variation of thecounterbalancing. Rings 42 can be used or removed as necessary tocounterbalance the arm.

A further ring 45 is captive on the forward end of cap 40; ring 45 willbe moved axially along section 31 of the arm when the milled ring 41 isrotated to adjust the counterbalancing but is held against rotation bymeans of a key way and grub screw arrangement, between the ring 45 andthe sleeve 37. The outer part of ring 45 carries a second milled ring 46to which is fastened an adjusting weight 48 (FIG. 4) of semicircularshape, so that by rotating the milled ring, with respect to the innerring portion 45, lateral balance of the arm can be adjusted.

To the forward end of section 31 of the arm is attached a crankedcoupling section 49. Section 49 has a tubular portion 50 which receivesthe rear end of a separable section 51 of the pickup arm. The tubularportion 50 carries one portion 52 of an electrical coupling, the otherpart 53 of which is carried by section 51 of the arm. The rear end ofsection 51 is a snug and vibration free fit in section 50 of thecoupling section. The forward end of section 51 carries the pickup head54. By applying gentle endwise pressure to the arm section 51, it can beseparated electrically and mechanically from the coupling member 50,thus permitting alternative pickup heads, each of which will be fittedwith its section 51 of pickup arm, as desired. By arranging the coupling52, 53 at the inward end of the pickup arm, the mass at the head of thearm is reduced, requiring a lesser counterweight and permitting acorrespondingly lighter arm construction. The coupling 52, 53 willnormally be located as near the vertical pivot axis as is convenient, itis desirable that the coupling should be at least within the inner halfof the length from the stylus to the vertical axis. There will be animprovement if only a short length of section 51 is attached to thehead.

Means may be provided for permitting slight angular adjustment for thecoupling member on section 31 of the arm so that the stylus may bedisposed vertically with respect to the record. Electrical connectionsto the socket member 52 pass first through an opening 55 in the couplingmember 50 and through section 31 of the arm, then through an opening 56(FIG. in the wall of section 31 and thence through the center of sleeve22, before emerging through the center of pillar 12.

Means are provided for varying the playing weight of the pickup. Cap 24,fastened to shaft 22, is fashioned to provide a sliding fit for a rod 60(FIG. 1), which bears two weights 61 and 62 at its respective ends. Therod carries gradations 63, with an index mark on cap 24. In use, the rod60 is moved to its initial or zero playing weight marking, and the armis then counterbalanced by adjustment of the main counterweight by meansof milled ring 41. The lateral arm balance can then be adjusted by ring46. In this condition, the arm will be precisely balanced and there willbe no downward force exerted at the stylus 64. To impose the desiredplaying weight at the stylus 64, the rod 60, with its weights, can nowbe moved forwardly, that is, to the left as viewed in FIG. 2;conveniently, each gradation 63 will correspond to a given increase ofplaying weight, such as 0.25 or 0.50 gram.

As a'result of the imposition of a playing weight at the stylus, a sidethrust will be created in the manner described above, of a magnitudewhich for a given installation is a fixed proportion of the playingweight. Conveniently, additional means may be provided whereby the sidethrust produced can be offset by giving to the pickup arm a further biastending to move it in the outward direction; the bias is adjustable andmust be adjusted for each change of playing weight.

However, with the pickup arm described, the axis of the shaft 22 is atan angle to the horizontal and the axis of the pivot defined by bearings32 will be correspondingly inclined to be vertical. As a result, theimposition of force at the stylus in the downward direction will beaccompanied by a lateral force, proportional to the downward force, andrelated to that downward force by the tangent of the angle that the axisof shaft 22 makes with the horizontal or, what is the same, the angle [3between the axis of bearings 32 and the vertical. By suitable choice ofthis angle and B being equal) the desired proportion can be obtainedbetween the horizontal and vertical forces imposed at the stylus by theplaying weight. Further the desired relationship between the downwardforce and the lateral force will be maintained for different settings ofthe playing weight adjustment afforded by slide rod 60. Any change ofplaying weight effected by means of the rod 60 will cause. acorresponding and appropriate change of the side thrust compensation.

As mentioned above, the relationship between the vertical force and theside thrust depends on certain factors in any given installation but mayvary somewhat from one pickup installation to another. It is thereforedesirable that the angle of the shaft 22 to the horizontal should beadjustable. To this end, the sleeve 21 is mounted on the pillar headassembly by means of a pillar screw 66, thus permitting the sleeve 21 torotate about the axis of the screw. Located in a recess in the sleeve 21is a plunger 67, loaded by a compression spring 68, and the plunger 67bears against the overhanging portion 69 of the pillar head assembly. Agrub screw 69a threaded into the overhanging portion 69 bears againstpart of the sleeve 21, so that by rotation of the grub screw 69a theangle of inclination of the shaft 22 can be varied, against thecompression of spring 68.

It is desirable that the playing weight adjustment system, includingshaft 22 and yoke 26, should be independently balanced, that is to say,if the pickup arm were released from the yoke bearings at 32 the partsincluding the shaft 22 and weights 61 and 62 should be at the positionof zero playing weight adjustment and the parts balanced about the axisof shaft 22. A facility of adjustment that is desirable in a pickup armin general, and essential in a versatile pickup arm, is a ready means ofadjusting the extent of overhang by varying the position of the verticalpivot axis of the arm with respect to the center of the recordturntable. With this object the bush 11 is mounted in a slot in the baseplate 10, and these two relatively movable parts are connected by athreaded rod 70 and engaging a nut 71 on the bush, with a milled screw72 on the rod; by rotation of the milled screw the position of the bushinn the slot can be varied and the overhang adjusted. Graduations 75 canbe provided to enable a given setting to be noted and reestablished.

Another desirable facility of adjustment is variation of the verticalheight of the pickup arm such as 51 above the motor board 16. In thepickup described, the pillar 12 is made vertically movable in bush l1,and the relative position of the two parts can be adjusted by a threadedrod 78, screw threaded into the bush, and rotatable in the pillar headassembly 20, by means of a milled knob 76.

It is also convenient to arrange for a lowering device for the arm. Forthis, an arm rest 77 can be fastened to a vertically movable part of thepillar head assembly 20, this arm being vertically movable, controlledby a dash pot, not shown, by suitable operating lever, which may extendfrom the assembly 20.

The pickup arms construction described is very advantageous in use. Itcan be adjusted for counterbalance, lateral balance, playing weight,vertical height, and overhang, and thus lends itself to use with a widevariety of pickup heads and cartridges. Change of playing weight isautomatically accompanied by the appropriate side thrust correction oncethe adjusting screw 70 has been adjusted. The pickup head can be rapidlychanged by the withdrawal of the arm 51, and the arrangement of theelectrical and mechanical couplings towards the rear part of the armreduces the head weight. The entire pickup assembly complete with thebase plate can be rapidly removed from the mounting plate, by virtue ofthe pegs M, a facility which is valuable with professional use f thepickup assembly. It is also an advantage that the pickup arm is crankedas appears more clearly from H6. 3, especially in conjunction with thefeature that the arm is pivoted by the offset arrangement, as appearsfrom FIG. 1. This permits of a low-compact construction.

What is claimed is: 1. A pickup arm assembly for reproducing sound froma disk type phonograph record supported by a rotatably driven generallyhorizontal turntable, comprising a. a pillar head assembly adapted forarrangement ad jacent said turntable; b. pickup arm means for supportingat one end a pickup cartridge (54) having a stylus (64)); 0. meansconnecting said pickup arm means with said pillar head assembly forvertical and horizontal pivotal movement, said connecting meansincluding 1. intermediate support means (22, 26) pivotally connectedwith said pillar head assembly for movement about a first generallyhorizontal pivot axis, and

2. means (32, 33) connecting said pickup arm means with saidintermediate support means for movement about a second pivot axis thatis inclined to the vertical by an acute angle (B):

d. counterbalance means (41, 416) balancing said pickup arm means to acounterbalanced condition relative to said generally horizontal pivotaxis; and

e. biasing means (60, 61, 62) for rotating said intermediate supportmember about its axis to impose on the stylus a selected downwardlydirected playing force that is automatically accompanied by acorresponding horizontally directed antiskating side thrust componentwhich is a function of said acute angle (,8).

2. Apparatus as defined in claim 1, wherein the first pivot axis isinclined to the horizontal by an acute angle (or) equal to said acuteangle ([3).

3. Apparatus as defined in claim 1, and further including third pivotmeans (66) connecting said intermediate support means with said pillarhead assembly for pivotal adjustment about a horizontal adjustment axisnormal to the vertical plane containing said first pivot axis, andadjustment means (690) for pivoting said intermediate support meansabout said horizontal adjustment axis to vary the angle of inclinationof said first pivot axis.

4. Apparatus as defined in claim 11, wherein said biasing means includesweight means (61, 62) radially adjustable relative to said intermediatesupport means.

5. Apparatus as defined in claim 1, and further including a base plate(10); and shaft means (E2) connecting said pillar head assembly to saidbase plate for vertical movement relative to said base plate.

6. Apparatus as defined in claim 5, and further including means ('78) oradjusting the height of said pillar head assembly and said shaft meansrelative to said base plate.

7. Apparatus as defined in claim 5, and further including meansincluding a sliding bush (11) for horizontally adjusting said shaftmeans and said pillar head assembly relative to said base plate.

8. Apparatus as defined in claim l, and further including means foradjusting the lateral balance of said pickup arm means, comprising aneccentrically weighted member (48) connected for coaxial rotationrelative to said pickup arm means.

9. Apparatus as defined in claim 8, wherein said counterbalance means isthreadably connected with said pickup arm means for axial adjustmentrelative thereto.

10. Apparatus as defined in claim 9, wherein said counterbalance meansincludes separable sections (42).

11. Apparatus as defined in claim 9, wherein said lateral balance weightmeans (48) is connected for axial displacement of said pickup arm meanssimultaneously with said counterbalance means.

12. Apparatus as defined in claim 11, .and further including meanspreventing rotational movement of said lateral balance weight meansrelative to said pickup arm means upon rotation of said counterbalancemeans.

13. Apparatus as defined in claim ll wherein said pickup arm meansincludes pickup head means 54 for supporting a stylus, said pickup headmeans including detachable electrical and mechanical coupling (52, 53)for the removal of said pickup head means from said arm means.

M. Apparatus as defined in claim 13, wherein said couplings are arrangedwithin the length of the arm, so that upon removal of the pickup headmeans, at least a part of the length of said arm means is removedtherewith.

115. Apparatus as defined in claim M, wherein said couplings arearranged in the inner half of the length of said arm means between thestylus and the arm pivot means.

16. Apparatus as defined in claim l, wherein said pickup arm means iscranked, the portion of the arm means near the pillar head assemblybeing lower in use than the stylus-supporting end portion of said armmeans.

17. Apparatus as defined in claim il, including a base plate attached tosaid pillar head assembly;

a fixed base support member (13); and locating and retaining means (1d,15) for locating and retaining said base plate relative to said basesupport member.

18. Apparatus as defined in claim 17, wherein said locating andretaining means includes pegs and cooperating sockets on the respectiveparts.

1. A pickup arm assembly for reproducing sound from a disk typephonograph record supported by a rotatably driven generally horizontalturntable, comprising a. a pillar head assembly (20) adapted forarrangement adjacent said turntable; b. pickup arm means (30) forsupporting at one end a pickup cartridge (54) having a stylus (64); c.means connecting said pickup arm means with said pillar head assemblyfor vertical and horizontal pivotal movement, said connecting meansincluding
 1. intermediate support means (22, 26) pivotally connectedwith said pillar head assembly for movement about a first generallyhorizontal pivot axis, and
 2. means (32, 33) connecting said pickup armmeans with said intermediate support means for movement about a secondpivot axis that is inclined to the vertical by an acute angle ( Beta ):d. counterbalance means (41, 46) balancing said pickup arm means to acounterbalanced condition relative to said generally horizontal pivotaxis; and e. biasing means (60, 61, 62) for rotating said intermediatesupport member about its axis to impose on the stylus a selecteddownwardly directed playing force that is automatically accompanied by acorresponding horizontally directed antiskating side thrust componentwhich is a function of saId acute angle ( Beta ).
 2. means (32, 33)connecting said pickup arm means with said intermediate support meansfor movement about a second pivot axis that is inclined to the verticalby an acute angle ( Beta ): d. counterbalance means (41, 46) balancingsaid pickup arm means to a counterbalanced condition relative to saidgenerally horizontal pivot axis; and e. biasing means (60, 61, 62) forrotating said intermediate support member about its axis to impose onthe stylus a selected downwardly directed playing force that isautomatically accompanied by a corresponding horizontally directedantiskating side thrust component which is a function of saId acuteangle ( Beta ).
 2. Apparatus as defined in claim 1, wherein the firstpivot axis is inclined to the horizontal by an acute angle ( Alpha )equal to said acute angle ( Beta ).
 3. Apparatus as defined in claim 1,and further including third pivot means (66) connecting saidintermediate support means with said pillar head assembly for pivotaladjustment about a horizontal adjustment axis normal to the verticalplane containing said first pivot axis, and adjustment means (69a) forpivoting said intermediate support means about said horizontaladjustment axis to vary the angle of inclination of said first pivotaxis.
 4. Apparatus as defined in claim 1, wherein said biasing meansincludes weight means (61, 62) radially adjustable relative to saidintermediate support means.
 5. Apparatus as defined in claim 1, andfurther including a base plate (10); and shaft means (12) connectingsaid pillar head assembly to said base plate for vertical movementrelative to said base plate.
 6. Apparatus as defined in claim 5, andfurther including means (78) or adjusting the height of said pillar headassembly and said shaft means relative to said base plate.
 7. Apparatusas defined in claim 5, and further including means including a slidingbush (11) for horizontally adjusting said shaft means and said pillarhead assembly relative to said base plate.
 8. Apparatus as defined inclaim 1, and further including means for adjusting the lateral balanceof said pickup arm means, comprising an eccentrically weighted member(48) connected for coaxial rotation relative to said pickup arm means.9. Apparatus as defined in claim 8, wherein said counterbalance means isthreadably connected with said pickup arm means for axial adjustmentrelative thereto.
 10. Apparatus as defined in claim 9, wherein saidcounterbalance means includes separable sections (42).
 11. Apparatus asdefined in claim 9, wherein said lateral balance weight means (48) isconnected for axial displacement of said pickup arm means simultaneouslywith said counterbalance means.
 12. Apparatus as defined in claim 11,and further including means preventing rotational movement of saidlateral balance weight means relative to said pickup arm means uponrotation of said counterbalance means.
 13. Apparatus as defined in claim1 wherein said pickup arm means includes pickup head means 54 forsupporting a stylus, said pickup head means including detachableelectrical and mechanical coupling (52, 53) for the removal of saidpickup head means from said arm means.
 14. Apparatus as defined in claim13, wherein said couplings are arranged within the length of the arm, sothat upon removal of the pickup head means, at least a part of thelength of said arm means is removed therewith.
 15. Apparatus as definedin claim 14, wherein said couplings are arranged in the inner half ofthe length of said arm means between the stylus and the arm pivot means.16. Apparatus as defined in claim 1, wherein said pickup arm means iscranked, the portion of the arm means near the pillar head assemblybeing lower in use than the stylus-supporting end portion of said armmeans.
 17. Apparatus as defined in claim 1, including a base plate (10)attached to said pillar head assembly; a fixed base support member (13);and locating and retaining means (14, 15) for locating and retainingsaid base plate relative to said base support member.
 18. Apparatus asdefined in claim 17, wherein said locating and retaining means includespegs and cooperating sockets on the respective parts.